KR20190058367A - Positive electrode material for lithium secondary battery, positive electrode and lithium secondary battery including the same - Google Patents

Abstract

The present invention relates to a positive electrode material, and a positive electrode and a lithium secondary battery comprising the same. The positive electrode material comprises: a first positive electrode active material represented by chemical formula 1, which is Li_a[Ni_bCo_cM^1_dM^a_e]O_2; and a second positive electrode active material represented by chemical formula 2, which is Li_x[Ni_yCo_zMn_wM^2_vM^b_u]_2. The positive electrode material has a bimodal particle size distribution including large diameter particles and small diameter particles, and the difference between the average particle size (D50) of the large diameter particles and small diameter particles is 3 μm or more. The positive electrode material according to the present invention is excllent in capacity characteristics.

Description

TECHNICAL FIELD [0001] The present invention relates to a positive electrode material for a lithium secondary battery, and a positive electrode and a lithium secondary battery including the same. BACKGROUND OF THE INVENTION [0002]

The present invention relates to a positive electrode material for a lithium secondary battery, a positive electrode including the same, and a lithium secondary battery.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density and voltage, a long cycle life, and a low self-discharge rate are commercially available and widely used.

Lithium transition metal composite oxides are used as the positive electrode active material of lithium secondary batteries. Among them, LiCoO ₂ Lithium cobalt composite metal oxide is mainly used. However, LiCoO ₂ has a poor thermal characteristic due to destabilization of crystal structure due to depolythium, and is expensive, so that it can not be used as a power source in fields such as electric vehicles.

Lithium manganese composite metal oxides (such as LiMnO ₂ or LiMn ₂ O ₄ ), lithium iron phosphate compounds (such as LiFePO ₄ ), or lithium nickel composite metal oxides (such as LiNiO ₂ ) have been developed as materials for replacing LiCoO ₂ . Among them, research and development of a lithium nickel composite metal oxide having a high reversible capacity of about 200 mAh / g and facilitating the realization of a large capacity battery are actively under way. However, LiNiO ₂ has a lower thermal stability than LiCoO _2, and if an internal short circuit occurs due to external pressure or the like in a charged state, the cathode active material itself is decomposed to cause rupture and ignition of the battery. Accordingly, a lithium nickel cobalt manganese oxide in which a part of Ni is substituted with Mn and Co has been developed as a method for improving the low thermal stability while maintaining excellent reversible capacity of LiNiO ₂ .

However, in the case of the lithium nickel cobalt manganese oxide, the rolling density of the particles is low. In particular, when the content of Ni is increased in order to increase the capacity, the rolling density of the particles is lowered and the energy density is lowered. When the electrode is strongly rolled in order to increase the rolling density, breakage of the current collector and cracking of the cathode material occur.

Further, in the case of lithium nickel cobalt manganese oxide having a high Ni content, there is a problem that the electrochemical performance such as high temperature service life is deteriorated due to low stability at high temperature.

Therefore, development of a cathode material having excellent energy density and capacity characteristics and excellent high-temperature lifetime characteristics is required.

A first technical object of the present invention is to provide a high-capacity cathode material excellent in high-temperature lifetime characteristics.

A second object of the present invention is to provide a positive electrode and a lithium secondary battery including the above-described cathode material.

In one aspect, the present invention is a cathode material comprising a first cathode active material represented by the following formula (1) and a second cathode active material represented by the following formula (2), wherein the cathode material is a bimodal And a difference in average particle diameter (D ₅₀ ) between the large diameter particles and small particle diameter particles is 3 μm or more.

[Chemical Formula 1]

Li _a [Ni _b Co _c M ¹ _d M ^a _e ] O ₂

In Formula 1, M ¹ is Mn, Al, Zr, or Mg, and M ^a is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Wherein at least one element selected from the group consisting of Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, 0.2, 0.01? D <0.2, 0? E? 0.02.

(2)

Li _x [Ni _y Co _z Mn _w M ² _v M ^b _u ] O ₂

In the formula 2, M ² is Al, Mg, Zr or Ti, and M ^b is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, And at least one element selected from the group consisting of Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, 0.2, 0.01? W <0.2, 0.01? V <0.2, 0? U?

At this time, the large diameter particles may have an average particle diameter (D ₅₀ ) of 10 μm to 20 μm, and the small particle diameter may have an average particle diameter (D ₅₀ ) of 1 μm to 7 μm.

In another aspect, the present invention provides a positive electrode comprising a positive electrode collector and a positive electrode active material layer formed on the positive electrode collector, wherein the positive electrode active material layer comprises the positive electrode material according to the present invention.

In another aspect, the present invention provides a positive electrode according to the present invention; cathode; A separator interposed between the anode and the cathode; And a lithium secondary battery including an electrolyte.

The cathode material according to the present invention is excellent in capacity characteristics using a lithium complex transition metal oxide having a nickel content of 80% or more, and has a bimodal particle size distribution, so that the rolling density and the energy density are high.

Further, the cathode material according to the present invention has excellent high-temperature lifetime characteristics as compared with the case of using a lithium nickel cobalt manganese oxide of a single composition by mixing two kinds of lithium composite transition metal oxides having different compositions.

FIG. 1 is a graph showing the high-temperature cycling characteristics of the lithium secondary battery produced by Examples 1 and 2 and Comparative Example 1. FIG.

Hereinafter, the present invention will be described in more detail.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may properly define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

In the present specification, the average particle diameter (D ₅₀ ) can be defined as the particle diameter at the 50% of the particle diameter distribution, and can be measured using a laser diffraction method. Specifically, the average particle diameter (D ₅₀ ) was measured by dispersing the target particles in a dispersion medium, introducing the dispersion into a commercially available laser diffraction particle size analyzer (for example, Microtrac MT 3000), irradiating ultrasound of about 28 kHz at an output of 60 W , The average particle diameter (D ₅₀ ) at 50% of the volume cumulative distribution along the particle diameter in the measuring apparatus can be calculated.

In the present specification, "%" means weight% unless otherwise specified.

As a result of intensive studies to develop a cathode material having both excellent capacity characteristics, energy density and high temperature lifetime characteristics, the present inventors have found that a cathode active material containing two kinds of cathode active materials having a specific composition, It has been found that the above object can be achieved by using a cathode material having a bimodal particle size distribution with a particle size particle and accomplishing the present invention.

Anode material

First, the cathode material according to the present invention will be described.

The cathode material according to the present invention includes a first cathode active material and a second cathode active material having different compositions, and has a bimodal particle size distribution including large diameter particles and small particle size particles. At this time, the difference between the average particle size (D ₅₀ ) of the large diameter particles and the small particle size particles may be 3 μm or more, preferably 3 μm to 15 μm, more preferably 3 μm to 10 μm.

The first cathode active material is a lithium complex transition metal oxide having a nickel content of 80 mol% or more. Specifically, it is a lithium complex transition metal oxide represented by the following Chemical Formula 1.

[Chemical Formula 1]

Li _a [Ni _b Co _c M ¹ _d M ^a _e ] O ₂

Wherein M ¹ is Mn, Al, Zr, or Mg, and M ^a is a doping element substituted in ^a transition metal (Ni, Co, and / or M ¹ ) And at least one element selected from the group consisting of Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, Or more.

The letter a means the molar ratio of lithium, and may be 0.9? A? 1.2, preferably 1.1? A? 1.2.

B means the molar ratio of nickel in the total transition metal, and can be 0.8? B <1, preferably 0.8? B? 0.98.

C means the molar ratio of cobalt in the total transition metals, and may be 0.01? C <0.2, preferably 0.01? C? 0.15.

Wherein d may be that the entire transition means the molar ratio of the metal M ^1, 0.01≤d <0.2, preferably, 0.01≤d≤0.15.

E means the molar ratio of the doping element M ^{a in} the total transition metal, and may be 0? E? 0.02, preferably 0? E? 0.01.

Specifically, the first cathode active material may include Li _a [Ni _b Co _c Mn _d ] O _{2 ,} Li _a [Ni _b Co _c Al _d ] O _{2 ,} Li _a [Ni _b Co _c Zr _d ] O ₂ , Li _a [Ni _b Co _c Mg _d ] O _{2 ,} Li _a [Ni _b Co _c Mn _d Al _e ] O _{2 ,} Li _a [Ni _b Co _c Mn _d Zr _e ] O ₂ , Li _a [Ni _b Co _c Mn _{d Mg e] O 2, Li} a [Ni b Co c Al d Zr e] O 2, or _{Li a [Ni b Co c Al} d Mg e] O 2, ( where, a, b, c, d and e Is the same as defined in Chemical Formula 1), but is not limited thereto.

The second cathode active material is a lithium complex transition metal oxide having a nickel content of 80 mol% or more, and specifically, a lithium complex transition metal oxide represented by the following Chemical Formula 2.

(2)

Li _x [Ni _y Co _z Mn _w M ² _v M ^b _u ] O ₂

In the above formula (2), M ² is Al, Mg, Zr or Ti, and M ^b is a doping element substituted in the transition metal (Ni, Co and / or M ¹ ) At least one element selected from the group consisting of Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, It can be an element.

X represents a molar ratio of lithium, and may be 0.9? X? 1.2, preferably 1.1? X? 1.2.

Y means the molar ratio of nickel and may be 0.8? Y <1, preferably 0.8? Y? 0.98.

Z means the molar ratio of cobalt and can be 0.01? Z <0.2, preferably 0.01? Z? 0.15.

W means the molar ratio of manganese, and may be 0.01? W <0.2, preferably 0.01? W? 0.1.

V means the molar ratio of M ² , and may be 0.01? V <0.2, preferably 0.01? V? 0.1.

The u could be that the entire transition means the molar ratio of the doping element M ^b of the metal, 0≤u≤0.02, preferably 0≤u≤0.01.

Specifically, the second cathode active material may include Li _x [Ni _y Co _z Mn _w Al _v ] O _{2 ,} Li _x [Ni _y Co _z Mn _w Mg _v ] O _{2 ,} Li _x [Ni _y Co _z Mn _w Zr _{v] O 2, Li x [} Ni y Co z Mn w Ti v] O 2, Li x [Ni y Co z Mn w Al v Mg u] O 2, Li x [Ni y Co z Mn w Al v Zr u ] O _{2 ,} or Li _x [Ni _y Co _z Mn _w Al _v Ti _u O ₂ where x, y, z, w, v are as defined in formula (2) It is not.

Meanwhile, the first cathode active material and / or the second cathode active material may further include a coating layer on the surface thereof, if necessary. At this time, the coating layer may be formed of at least one of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, And at least one coating element selected from the group consisting of one or more elements selected from the group consisting of S, When such a coating layer is formed, the contact between the positive electrode active material and the electrolyte solution is blocked, thereby suppressing the occurrence of side reactions, so that it is possible to improve the lifetime characteristics when applied to a battery and increase the filling density of the positive electrode active material.

As described above, when the coating element is further included, the content of the coating element in the coating layer may be from 100 ppm to 10,000 ppm, preferably from 200 ppm to 5,000 ppm, based on the total weight of the cathode active material.

The coating layer may be formed on the entire surface of the cathode active material, or may be partially formed. Specifically, when the coating layer is partially formed on the surface of the cathode active material, an area of 5% or more and less than 100%, preferably 20% or more and less than 100% of the total surface area of the cathode active material may be formed.

On the other hand, the first cathode active material and the second cathode active material may be formed such that the content of the transition metal elements in the active material particle may be constant regardless of the position, and the content of one or more metal elements may be changed It is possible. For example, the cathode active material may have a concentration gradient in which at least one of Ni, Mn, Co, M ^1, and M ² gradually changes, and the 'gradually changing concentration gradient' Is present in a concentration distribution that changes continuously or stepwise in the entire particle or in a specific region.

Since the first cathode active material and the second cathode active material both contain 80 mol% or more of nickel, excellent capacity characteristics can be realized. Also, according to the studies of the present inventors, when the cathode active material of Formula 1 and the cathode active material of Formula 2 are mixed as described above, the lifetime characteristics at high temperature are improved.

Meanwhile, the cathode material of the present invention is prepared by mixing the first cathode active material and the second cathode active material in a weight ratio of 10:90 to 90:10, preferably 20:80 to 80:20, more preferably 30:70 to 70:70 : 30 weight ratio. When the mixing ratio of the first cathode active material and the second cathode active material satisfies the above range, a high electrode density can be obtained.

On the other hand, the cathode material of the present invention has a bimodal particle size distribution including large-diameter particles and small particle size particles having different average particle diameters (D ₅₀ ). When the bimodal particle size distribution is thus obtained, the void space between the large diameter particles is filled with small particle size particles at the time of rolling, so that a high rolling density and an energy density can be realized.

At this time, the difference between the average particle size (D ₅₀ ) of the large diameter particles and the small particle size particles may be 3 μm or more, preferably 3 μm to 15 μm, more preferably 3 μm to 10 μm. When the difference between the average diameter (D ₅₀ ) of the large diameter particles and the small diameter particles satisfies the above range, the small diameter particles are well filled between the large diameter particles and the rolling density and the energy density are improved.

Specifically, the large diameter particles may have an average particle diameter (D ₅₀ ) of 10 μm to 20 μm, preferably 11 to 18 μm, more preferably 12 to 18 μm. The particle size of the small particle size may be 1 μm to 7 μm, preferably 2 μm to 7 μm, more preferably 3 μm to 6 μm, on the average particle size (D ₅₀ ).

On the other hand, the kind of the active material constituting the small particle size particles and the large particle size particles is not particularly limited and may be the first positive electrode active material and / or the second positive electrode active material.

According to one embodiment, the cathode material of the present invention may be such that the first cathode active material constitutes large particle particles and the second cathode active material constitutes small particle particles.

According to another embodiment, the cathode material of the present invention may be such that the first cathode active material constitutes small particle size particles and the second cathode active material constitutes large particle particles.

According to another embodiment, the cathode material of the present invention may have a bimodal particle size distribution in which at least one of the first cathode active material and the second cathode active material includes both the large-diameter particles and the small particle size particles.

anode

Next, the anode according to the present invention will be described.

The positive electrode according to the present invention includes a positive electrode collector and a positive electrode active material layer formed on the positive electrode collector, wherein the positive electrode active material layer includes the positive electrode material according to the present invention, / &Lt; / RTI &gt; binder.

In this case, the cathode material is the same as described above, and may be contained in an amount of 80 to 99% by weight, more specifically 85 to 98.5% by weight based on the total weight of the cathode active material layer. When the anode material is included in the above range, excellent capacity characteristics can be exhibited.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, carbon, nickel, titanium, , Silver or the like may be used. In addition, the cathode current collector may have a thickness of 3 to 500 탆, and fine irregularities may be formed on the surface of the current collector to increase the adhesive strength of the cathode material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The conductive material is used for imparting conductivity to the electrode. The conductive material is not particularly limited as long as it has electron conductivity without causing chemical change. Specific examples thereof include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black and carbon fiber; Metal powder or metal fibers such as copper, nickel, aluminum and silver; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; And polyphenylene derivatives. These may be used alone or in admixture of two or more. The conductive material may be included in an amount of 0.1 to 15% by weight based on the total weight of the cathode active material layer.

The binder serves to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, Polypropylene, ethylene-propylene-diene polymer (EPDM), sulphonated-EPDM, polyvinylpyrrolidone, polyvinylpyrrolidone, polyvinylpyrrolidone, Styrene-butadiene rubber (SBR), fluorine rubber, and various copolymers thereof, and one kind or a mixture of two or more kinds of them may be used. The binder may be included in an amount of 0.1 to 15% by weight based on the total weight of the cathode active material layer.

The positive electrode of the present invention can be produced according to a conventional positive electrode manufacturing method, except that the positive electrode material according to the present invention is used as the positive electrode active material. Specifically, it can be produced by applying a positive electrode material prepared by dissolving or dispersing a positive electrode material, a binder and / or a conductive material in a solvent onto a positive electrode collector, followed by drying and rolling.

The solvent may be any solvent commonly used in the art and may be a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or water . One of these may be used alone, or a mixture of two or more thereof may be used. The amount of the solvent to be used is not particularly limited as long as it can be adjusted to have an appropriate viscosity in consideration of the coating thickness of the positive electrode composite material, the production yield, workability, and the like.

Alternatively, the positive electrode may be produced by casting the positive electrode composite material on a separate support, and then peeling off the support from the support to laminate a film on the positive electrode collector.

Lithium secondary battery

Next, a lithium secondary battery according to the present invention will be described.

The lithium secondary battery of the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is the same as the positive electrode according to the present invention. Therefore, a detailed description of the positive electrode will be omitted and only the remaining configuration will be described below.

The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, Carbon, nickel, titanium, silver or the like, aluminum-cadmium alloy, or the like may be used. In addition, the negative electrode collector may have a thickness of 3 to 500 탆, and similarly to the positive electrode collector, fine unevenness may be formed on the surface of the collector to enhance the binding force of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The anode active material layer optionally includes a binder and a conductive material together with the anode active material.

As the negative electrode active material, various negative electrode active materials used in the related art can be used, and there is no particular limitation. Specific examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon; Metal compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys or Al alloys; _{SiO β (0 <β <2} ), SnO 2, vanadium oxide, which can dope and de-dope a lithium metal oxide such as lithium vanadium oxide; Or a composite containing the above-described metallic compound and a carbonaceous material such as a Si-C composite or a Sn-C composite, and any one or a mixture of two or more thereof may be used. Also, a metal lithium thin film may be used as the negative electrode active material. As the carbon material, both low crystalline carbon and highly crystalline carbon may be used. Examples of the low-crystalline carbon include soft carbon and hard carbon. Examples of the highly crystalline carbon include natural graphite, artificial graphite, artificial graphite or artificial graphite, Kish graphite graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar coke derived cokes).

On the other hand, the negative electrode active material may include 80% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

The binder is a component for assisting the bonding between the conductive material, the active material and the current collector, and is usually added in an amount of 0.1% by weight to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene Examples thereof include ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluorine rubber and various copolymers thereof.

The conductive material may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer, as a component for further improving the conductivity of the negative electrode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The negative electrode active material layer is prepared by applying and drying a negative electrode active material prepared by dissolving or dispersing a negative active material on a negative electrode current collector and optionally a binder and a conductive material in a solvent or by drying the negative electrode active material on a separate support And then laminating a film obtained by peeling from the support onto an anode current collector.

Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode to provide a passage for lithium ion, and can be used without any particular limitation as long as it is used as a separator in a lithium secondary battery. Particularly, It is preferable that the electrolyte membrane has a low resistance to water and an excellent ability to impregnate electrolytes. Specifically, porous polymer films such as porous polymer films made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers and ethylene / methacrylate copolymers, May be used. Further, a nonwoven fabric made of a conventional porous nonwoven fabric, for example, glass fiber of high melting point, polyethylene terephthalate fiber, or the like may be used. In order to secure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and the separator may be selectively used as a single layer or a multilayer structure.

As the electrolyte used in the present invention, there can be used an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, and a molten inorganic electrolyte which can be used for a lithium secondary battery, .

Specifically, the electrolyte may include an organic solvent and a lithium salt.

The organic solvent may be used without limitation as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate,? -Butyrolactone and? -Caprolactone; Ether solvents such as dibutyl ether or tetrahydrofuran; Ketone solvents such as cyclohexanone; Aromatic hydrocarbon solvents such as benzene and fluorobenzene; Dimethyl carbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate PC) and the like; Alcohol solvents such as ethyl alcohol and isopropyl alcohol; Ra-CN (Ra is a linear, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double bond aromatic ring or ether bond); Amides such as dimethylformamide; Dioxolanes such as 1,3-dioxolane; Or sulfolane may be used. Among these, a carbonate-based solvent is preferable, and a cyclic carbonate (for example, ethylene carbonate or propylene carbonate) having a high ionic conductivity and a high dielectric constant, for example, such as ethylene carbonate or propylene carbonate, For example, ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1: 1 to 9, the performance of the electrolytic solution may be excellent.

The lithium salt may be used, without limitation, those which are commonly used in a lithium secondary battery electrolyte, such as an anion, and containing the Li ⁺ in the lithium salt cation is F ^-, Cl ^-, Br ^-, I ^-, NO _{^{3 -, N (CN) 2}} -, BF 4 -, ClO 4 -, AlO 4 -, AlCl 4 -, PF 6 -, SbF 6 -, AsF 6 -, BF 2 C 2 O 4 -, BC 4 O 8 _{^{-, PF 4 C 2 O 4}} -, PF 2 C 4 O 8 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 _{^{PF -, (CF 3) 6}} P -, CF 3 SO 3 -, C 4 F 9 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N - _{, CF 3 CF 2 (CF 3} ) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- . Specifically, the lithium salt may be LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCH ₃ CO ₂ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiAlO ₄ , and LiCH ₃ SO ₃ , or a mixture of two or more thereof. In addition to these, lithium bisperfluoroethanesulfonimide (LiBETI) (Li ₂ N ₂ (SO ₂ C ₂ F ₅ ) ₂ ), a lithium imide salt represented by LiFSI (lithium fluorosulfonyl imide, LiN (SO ₂ F) ₂ ) and LiTFSI (lithium bis trifluoromethanesulfonimide, LiN (SO ₂ CF ₃ ) ₂ ) Can be used. Specifically, the electrolyte salt is _{LiPF 6, LiBF 4, LiCH 3} CO 2, LiCF 3 CO 2, LiCH 3 SO 3, LiFSI, LiTFSI and _{LiN (C 2 F 5 SO 2} ) danilmul selected from the group consisting of ₂ or two or more of And mixtures thereof.

The lithium salt can be appropriately changed within a range that is usually usable, but it can be specifically contained in the electrolyte in an amount of 0.8 M to 3 M, specifically 0.1 M to 2.5 M.

In addition to the electrolyte components, various additives may be added to the electrolyte for the purpose of improving lifetime characteristics of the battery, suppressing the reduction of the battery capacity, and improving the discharge capacity of the battery. Such additives include, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate and the like; N, N &lt; RTI ID = 0.0 &gt; (N, &lt; / RTI &gt; N, N'-tetramethyluronium hexafluorophosphate), pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride, and the above additives may be used singly or in combination. The additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

The lithium secondary battery according to the present invention can be used for portable equipment such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEV).

According to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell and a battery pack including the same.

The battery module or the battery pack may include a power tool; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); Or a power storage system, as shown in FIG.

The external shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells.

Hereinafter, the present invention will be described in detail by way of examples with reference to the following examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

Example  One

LiNi ₀ having an average particle diameter (D ₅₀ ) of 5 탆 _{. 8} Co _{0 . 1} Mn _{0 . 1} O ₂ and LiNi _0.83 Co _0.11 Mn _0.04 Al _0.02 O ₂ having an average particle diameter (D ₅₀ ) of 15 탆 was mixed at a weight ratio of 30:70 to form a cathode material A.

The positive electrode material A, the carbon black conductive material, and the PVdF binder prepared above were mixed at a weight ratio of 96: 2: 2 and mixed in an NMP solvent to prepare a positive electrode mixture. The positive electrode composite material was applied to an aluminum foil having a thickness of 12 占 퐉, dried, and then rolled to produce a positive electrode.

On the other hand, graphite, a carbon conductive material (SuperC65) and a PVdF binder were mixed as a negative electrode active material at a weight ratio of 95.6: 0.75: 3.65, and this was added to NMP as a solvent to prepare a negative electrode material. The negative electrode material was coated on a copper foil having a thickness of 20 占 퐉, dried, and then rolled to produce a negative electrode.

The positive electrode and the negative electrode prepared above were laminated together with a polyolefin separator to produce an electrode assembly. The electrode assembly was placed in a battery case and mixed with 100 parts by weight of a mixed solvent of ethylene carbonate: propyl propionate: diethyl carbonate in a ratio of 3: 1: 6 An electrolyte solution in which 1 M of LiPF ₆ , 0.5 part of vinylene carbonate (VC) and 1.0 part of 1-3 of propane sultone (PS) had been dissolved was injected into a lithium secondary battery.

Example  2

LiNi ₀ having an average particle diameter (D ₅₀ ) of 15 μm _{. 8} Co _{0 . 1} Mn _{0 . 1} O ₂ and LiNi _0.83 Co _0.11 Mn _0.04 Al _0.02 O ₂ having an average particle diameter (D ₅₀ ) of 5 탆 was mixed at a weight ratio of 70:30 to form a cathode material B.

A lithium secondary battery was produced in the same manner as in Example 1, except that the cathode material B prepared as described above was used instead of the cathode material A.

Example  3

LiNi ₀ having an average particle diameter (D ₅₀ ) of 10 μm _{. 8} Co _{0 . 1} Mn _{0 . 1} O ₂ and LiNi _0.83 Co _0.11 Mn _0.04 Al _0.02 O ₂ having an average particle diameter (D ₅₀ ) of 5 μm was mixed at a weight ratio of 70:30 to form a cathode material C.

A lithium secondary battery was produced in the same manner as in Example 1, except that the cathode material C prepared as described above was used instead of the cathode material A.

Example  4

LiNi ₀ having an average particle diameter (D ₅₀ ) of 13 탆 _{. 8} Co _{0 . 1} Mn _{0 . 1} O ₂ and LiNi _0.83 Co _0.11 Mn _0.04 Al _0.02 O ₂ having an average particle diameter (D ₅₀ ) of 5 탆 was mixed at a weight ratio of 70:30 to form a cathode material D.

A lithium secondary battery was prepared in the same manner as in Example 1, except that the cathode material D prepared as described above was used in place of the cathode material A.

Example  5

LiNi ₀ having an average particle diameter (D ₅₀ ) of 15 μm _{. 85} Co _{0 . 1} Mn _{0 . 05} O ₂ and LiNi _0.83 Co _0.11 Mn _0.05 Mg _0.01 O ₂ having an average particle diameter (D ₅₀ ) of 5 탆 was mixed at a weight ratio of 70:30 to form a cathode material E.

A lithium secondary battery was prepared in the same manner as in Example 1, except that the cathode material E prepared as described above was used instead of the cathode material A.

Comparative Example  One

LiNi ₀ having an average particle diameter (D ₅₀ ) of 15 μm _{. 8} Co _{0 . 1} Mn _{0 . 1} O ₂ and LiNi _0.8 Co _0.1 Mn _0.1 O ₂ having an average particle diameter (D ₅₀ ) of 5 탆 was mixed at a weight ratio of 70:30 to form a cathode material F.

A lithium secondary battery was produced in the same manner as in Example 1, except that the cathode material F prepared as described above was used instead of the cathode material A.

Comparative Example  2

LiNi ₀ having an average particle diameter (D ₅₀ ) of 6 탆 _{. 8} Co _{0 . 1} Mn _{0 . 1} O ₂ and LiNi _0.83 Co _0.11 Mn _0.04 Al _0.02 O ₂ having an average particle diameter (D ₅₀ ) of 8 μm was mixed at a weight ratio of 70:30 to form a cathode material G.

A lithium secondary battery was produced in the same manner as in Example 1, except that the cathode material G prepared as described above was used instead of the cathode material A.

Comparative Example  3

LiNi ₀ having an average particle diameter (D ₅₀ ) of 15 μm _{. 8} Co _{0 . 1} Mn _{0 . 1} O ₂ and LiNi _0.83 Co _0.11 Mn _0.04 Al _0.02 O ₂ having an average particle diameter (D ₅₀ ) of 15 μm was mixed at a weight ratio of 70:30 to form a cathode material H.

A lithium secondary battery was produced in the same manner as in Example 1, except that the cathode material H prepared as described above was used instead of the cathode material A.

Comparative Example  4

LiNi ₀ having an average particle diameter (D ₅₀ ) of 5 탆 _{. 8} Co _{0 . 1} Mn _{0 . 1} O ₂ and LiNi _0.83 Co _0.11 Mn _0.04 Al _0.02 O ₂ having an average particle diameter (D ₅₀ ) of 5 μm was mixed at a weight ratio of 30:70 to form a cathode material I.

A lithium secondary battery was produced in the same manner as in Example 1, except that the cathode material I prepared as described above was used instead of the cathode material A.

Comparative Example  5

LiNi ₀ having an average particle diameter (D ₅₀ ) of 5 탆 _{. 6} Co _{0 . 2} Mn _{0 . 2} O ₂ and LiNi _0.83 Co _0.11 Mn _0.04 Al _0.02 O ₂ having an average particle diameter (D ₅₀ ) of 15 μm was mixed at a weight ratio of 30:70 to form a cathode material J.

A lithium secondary battery was prepared in the same manner as in Example 1, except that the positive electrode material J was used instead of the positive electrode material A as described above.

Comparative Example  6

LiNi ₀ having an average particle diameter (D ₅₀ ) of 5 탆 _{. 8} Co _{0 . 1} Mn _{0 . 1} O ₂ and LiNi _0.6 Co _0.2 Mn _0.2 O ₂ having an average particle diameter (D ₅₀ ) of 15 μm was mixed at a weight ratio of 30:70 to form a cathode material K.

A lithium secondary battery was prepared in the same manner as in Example 1, except that the cathode material K prepared as described above was used instead of the cathode material A.

Experimental Example  One

The lithium secondary batteries manufactured in Examples 1 to 5 and Comparative Examples 1 to 6 were charged and maintained at 45 ° C in the range of 2.5 to 4.2 V under 0.3 C / %) And resistance increase rate (%) were measured. The measurement results are shown in Table 1. In addition, FIG. 1 is a graph showing the cycle characteristics of the lithium secondary batteries manufactured in Examples 1 and 2 and Comparative Example 1.

100 cycles 200 cycles Capacity retention rate (%) Rate of resistance increase (%) Capacity retention rate (%) Rate of resistance increase (%) Example 1 92.5 9.6 88.5 18.8 Example 2 92.4 14.0 88.6 23.7 Example 3 90.8 19.8 85.9 30.5 Example 4 91.2 16.9 86.4 27.4 Example 5 90.3 21.4 85.2 34.2 Comparative Example 1 90.4 23.2 84.8 37.4 Comparative Example 2 87.1 29.2 80.0 44.3 Comparative Example 3 86.9 29.8 79.4 44.9 Comparative Example 4 85.4 30.7 78.7 46.1 Comparative Example 5 88.1 27.7 82.2 39.7 Comparative Example 6 88.2 27.3 82.4 40.8

As shown in [Table 1] and Fig. 1, it is preferable to use two kinds of cathode active materials satisfying the composition of the present invention, and the difference in average particle diameter (D ₅₀ ) between large- The secondary batteries of Examples 1 to 5 using the positive electrode material having the positive electrode material of Comparative Examples 1 to 6 showed better high temperature cycle characteristics than those of the secondary batteries of Comparative Examples 1 to 6. Especially, as the number of cycles increased, As shown in FIG.

Claims (12)

1. A cathode material comprising a first cathode active material represented by the following formula (1) and a second cathode active material represented by the following formula (2)
Wherein the cathode material has a bimodal particle size distribution including large-diameter particles and small particle size particles,
Wherein the difference between the average particle diameter (D ₅₀ ) of the large-diameter particles and the small particle diameter is 3 μm or more.
[Chemical Formula 1]
Li _a [Ni _b Co _c M ¹ _d M ^a _e ] O ₂
In Formula 1, M ¹ is Mn, Al, Zr, or Mg, and M ^a is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Wherein at least one element selected from the group consisting of Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, 0.2, 0.01? D <0.2, 0? E? 0.02.

(2)
Li _x [Ni _y Co _z Mn _w M ² _v M ^b _u ] O ₂
In the formula 2, M ² is Al, Mg, Zr or Ti, and M ^b is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, And at least one element selected from the group consisting of Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, 0.2, 0.01? W <0.2, 0.01? V <0.2, 0? U?
The method according to claim 1,
Wherein the large-diameter particles have an average particle diameter (D ₅₀ ) of 10 μm to 20 μm.
The method according to claim 1,
Wherein the small particle size particles have an average particle diameter (D ₅₀ ) of 1 to 7 μm.
The method according to claim 1,
Wherein the first cathode active material is the small particle particle and the second cathode active material is the large particle particle.
The method according to claim 1,
Wherein the first cathode active material is the large particle particle and the second cathode active material is the small particle particle.
The method according to claim 1,
Wherein at least one of the first cathode active material and the second cathode active material has a bimodal particle size distribution including the large-diameter particles and the small particle size particles.
The method according to claim 1,
Wherein the first cathode active material and the second cathode active material are contained in a weight ratio of 10:90 to 90:10.
The method according to claim 1,
Wherein at least one of the first cathode active material and the second cathode active material is selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, And at least one coating element selected from the group consisting of Mo, Sr, Sb, Bi, Si, and S.
The method according to claim 1,
In Formula 1, M ¹ is Mn,
Wherein M &lt; 2 ^&gt; is Al in the formula (2).
The method according to claim 1,
Wherein a difference between an average particle diameter (D ₅₀ ) of the large-diameter particles and small particle size particles is 3 μm to 15 μm.
A positive electrode collector, and a positive electrode active material layer formed on the positive electrode collector,
Wherein the cathode active material layer comprises the cathode material according to any one of claims 1 to 10.
A cathode of claim 11;
cathode;
A separator interposed between the anode and the cathode; And
A lithium secondary battery comprising an electrolyte.

Images